Retractable hard formation drill bit



Sept. 25, 1956 J. M. CAMP RETRACTABLE HARD FORMATION DRILL BIT 5Sheets-Sheet 1 Filed Jan. 29, 1952 QfOhfl cam/Q sax/ember Qbboraeg Sept.25, 1956 J. M. CAMP RETRACTABLE HARD FORMATION DRILL BIT 3 Sheets-Sheet2 John m. (amp 'lrzvenbor Q5 Z0, CLbuorrzeg Filed Jan. 29, 1952 Sept.25, 1956 J. M. CAMP RETRACTABLE HARD FORMATION DRILL BIT s sheets-sheet3 Filed Jan. 29, 1952 A w m 4 m 7/74/ 7 a n M a m m v. :2: k m 4/ & 5

F I G doho. 11 2. Camp Sam a mbgw m Qubornas 2,764,388 Patented Sept.25, 1956 RETRACTABLE FORMATION DRILL BIT John M. Camp, Tulsa, Okla.,assignor to Esso Research and Engineering (Iompany, a corporation ofDelaware Application January 29, 1952, Serial No. 268,891

6 Claims. (Cl. 25561) This invention concerns a novel and improved formof retractable drill bit. The drill bit of this invention is adapted tobe lowered through a drill stem for expension and clamping in a drillcollar at the lower end of the drill string. The drill expands in such amanner as to lock a plurality of cone-type hard formation cutters at thelower termination of the drill collar so as to drill a borehole largerin diameter than the drill string. The bit includes provisions enablingrelease of the bit at the bottom of the drill collar and permitting thebit to be pulled upwardly through the drill string as, for example, bymeans of a wire line spearhead retriever.

it has long been appreciated that a desirable form of drill bit for usein oil exploration would be a bit which could be placed in cuttingposition and could be periodically retracted and returned to the surfaceof the earth without necessitating removal of the drill string from theborehole. Such a bit is particularly attractive in minimizing the timeand expense of pulling a drill string from a well bore and of againrunning the drill string into the bore hole Whenever necessary toreplace or recondition a drill bit. There have been a variety ofsuggestions as to bits of this general character. However, the problemsinvolved in providing an entirely suitable retractable drill bit aresufiiciently difiicult so that there has been a demand for an improvedtype of retractable drill bit.

The present invention is concerned with this objective and provides adesirable form of expansible bit overcoming many of the disadvantages ofpresently known drill bits of this character. For example, as will bebrought out, the drill of this invention employs a drill collar which isfree of internal slots or grooves which would be subject to disablingplugging by drill cuttings, sediment, etc. Again, for example, provisionis made to transfer torsion from the drill stem to the cutters withoutnecessitating use of a slotted drill collar or the like, imposingundesired stress limitations. These and other advantages of the noveldrill bit herein disclosed may be appreciated from the followingdescription.

The retractable drill bit of this invention utilizes a tubular drillcollar in which a cylindrical mandrel element is slidably maintained. Anumber of longitudinal slots or grooves are cut in the mandrel elementcorresponding in number to the cone cutters to be employed. A slidingsupport member for each of the cone cutters is arranged for longitudinalmovement in the grooves of the mandrel within the limits of the drillcollar. The cone cutter support members are slidably fastened to themandrel element. A suitable arrangement of latching dogs and matingshoulders on the diiferent elements described is employed to controlpositioning of cone cutters for both retraction of the cutters into thedrill collar and for expansion of the cone cutters through the lower endof the drill collar. In the expanded position, a tapered portion of themandrel element acts with a tapered section of the drill collar to forma wedge-shaped aperture in which the cone cutters can be wedged in orderto transmit torque directly from the drill collar to the cone cuttersfor drilling purposes.

The appended drawings illustrate a preferred embodiment of the drill bitof this invention illustrating as Well a number of desirable featureswhich may be included in the apparatus. It should be observed that forsimplicity the drawings have been prepared to illustrate a retractablehard formation drill bit having two cone cutters. In actuality it ispreferred to employ three cone cutters but the principles of operationcan better be understood by considering a drill bit employing two conecutters.

Figure 1 of the drawings illustrates the drill of this invention inelevational cross-sectional detail, showing the drill bit in an extendedand locked drilling position in the drill collar;

Figure 2 is a right side view of the drill bit, showing the drill collarin cross section;

Figure 3 is a cross-sectional elevational view of the lower portion ofthe drill bit in retracted position;

Figure 4 is a cross-section view of the apparatus of Figure 2 along theline IV-IV;

Figure 5 is a cross-section of Figure 1 along the line V-V;

Figure 6 is a detailed cross-sectional elevational view of a preferredarrangement of the upper portion of the drill;

Figure 7 is a view of a suitable fishing tool for use with the drill bitilllustrated, permitting the bit to be lowered into position andpermitting recovery of the drill bit, and;

Figure 8 is a fragmentary view corresponding to a portion of Figure 2 inwhich the two circumferential grooves or recesses have been replaced bya single circumferential recess.

Referring now to Figure 1, a drill collar is designated by the numeral 1which is of novel design to cooperate with the drill bit illustrated.Drill collar 1 may be fixed to a conventional casing or drill string bymeans of suitable threaded couplings. The drill collar will havesubstantially the same internal diameter as the drill stem with whichthe drill is to be operated. Preferably, however, the external diameterof the drill collar 1 is somewhat enlarged so as to provide a thickerwalled drill collar. member of substantial wall thickness to provide thenecessary strength required to drive the drill bit fixed within thisdrill collar. The lower and inner termination of the drill collar isprovided with an outwardly and downwardly opening enlargement. Thisserves to provide a downwardly and outwardly open taper 3 against whichthe drill cutters may be wedged as will be described. Twocircumferential grooves or recesses 4 and 5 are machined in the drillcollar to accommodate latching dogs positioned on the drill bit. Asdescribed therefore, the drill collar simply comprises a tubular memberhaving circumferential grooves 4 and 5 and provided with an outwardlyflared opening 3. The drill collar is notable for the absence of anylongitudinal slots or grooves and by its simplicity of construction.

Fitting within the drill collar 1 is a retractable drill bit essentiallycomprising three elements. An inner mandrel '8 constitutes the centralportion of the drill bit having a diameter somewhat less than theinternal diameter of the drill collar. The mandrel 8 is provided withtwo diametrically opposed longitudinal grooves or slots extendingsubstantially the length of the mandrel. These grooves are best shown inFigures 2 and 4 and are identified by numerals 1 1 and '12. Fittingwithin the grooves 11 and 12 are the two remaining principal elements ofthe drill bit consisting of slidable sections 13 and 14. As will bedescribed, each of the slidable sec- The drill collar simply comprises atubular 3 tions 16 and 14 is free to slide upwardly or downwardly withrespect to mandrel 8 in the groove or slot provided to the extentpermitted by the latching dogs and mating shoulders provided on slidingsections 13 and 1'4 and mandrel 8.

Each of the sliding sections l '3 and 14 serves as a supporting andguiding member for the cone cutters ill) which are suspended from themand will hereinafter be identified .as cone cutter guide members. Thecone cutters of conventional design may be suspended from the guidemembers by the straps or suspension arms 15. A pivot pin 16 passingthrough the lower termination of each suspension arm and passing througheach cone cutter 10 serves to permit pivotal movement of the conecutters within the drill collar. Downward movement of each guide member'13 or :14, with respect to the drill collar is limited by latching dogs6 which are pivotally fixed to each sliding element and are arranged tobear against the upward facing bearing surface of the annular groove 5machined in the drill collar. Each of the latching dogs 6 is urgedoutwardly into latching position by means of leaf springs 7. Thelatching dogs 6 are provided with inward extensions, shaped to mate witha recess 20 or 21 cut in the slotted portions of mandrel 8. Theextensions of the latching dogs may thus fit within the recesses 20 and21 when the dogs are forced into these recesses, permitting the latchingdogs to lie flush with the periphery of the mandrel.

The lower portion of guide member 18 has cutaway inner portion so as toprovide a shoulder 23 positioned some distance below latching dog 6. Thelower termination of slot 11 of mandrel 8 is built out somewl'xat so asto provide .a shoulder 24 adjacent the lower portion of the mandrel. Aswill be described, shoulder 2'4 is adapted to meet shoulder 23 so as tolimit downward movement of guide member 11 3 with respect to the mandrel8. Guide member 14- is similarly provided with a shoulder 25, which,however is positioned at a diii-ere-nt distance below latching dog 6fixed to guide member. Again, shoulder 25 is adapted to bear on ashoulder 26 provided in the slot 12 of the mandrel 8.

The lowermost portion of each guide slot 11 and 12 of the mandrel is cutaway more deeply to form a bed in the slot which is tapered inwardly.When the drill is in the position shown in Figure 1, the tapered shanksof cone cutters '10 tit against the taper of the slots referred to. Thewedge shaped shank of the cone cutters there- -fore wedges tightlybetween the drill collar 1 and the mandrel 8 when weight is placed onthe cone cutters.

In order to maintain the mandrel in a locked downward position tomaintain the cone .cutters in the positions illustrated in Figure l1when weight is applied to them, latching dogs 30 are provided at theupper end of the mandrel 8. These latching dogs are pivoted in slots ofthe mandrel and are normally urged outwardly by leaf springs 31 asbetter shown in Figure 6. The latching dogs will thus be forced into thecircumferential recess 4 of the drill collar when registered therewithso as to bear against the downward facing bearing surface in groove 4and thus lock the mandrel 8 against upward movement with respect todrill collar 1. It is apparent that when the mandrel has been forceddownwardly suificiently far to permit the latching dogs Bil to springoutwardly into the latching position illustrated, the drill cutters 11dwill be locked into the expanded position shown in Figures 1 and 2 so asto permit drilling.

The inner portions of the latching dogs '30 are provided with recess-es36 which may close over the spearhead 37 ot,a retrieving tool when thelatching dogs 30 are forced inwardly.

With this description of the general arrangement of the elements of theretractable drill bit illustrated, the operation of this drill bit maynow be understood. Assuming that the drill bit is in the extendeddrilling position illustrated in Figure 1, operation of the elements 4will be described as the drill bit is forced into retracted position forremoval from the drill string.

In order to retract the drill bit of Figure 1, a retrieving tool havinga suitable spearhead 37 is lowered into the drill string by means of awire line or cable. As will be brought out in connection with Figure 7of the drawings, the retrieving tool in addition to the spearhead 37must have tapered surfaces of a nature to force the latching dogs 30inwardly over the spearhead to permit the latches 34) to pass upwardlyinto the drill string while preventing release of the spearhead from therecesses 36 provided in the latching dogs. When the latches have beenforced to this position, spearhead 37 may be pulled upwardly through thedrill collar and drill string together with the drill b it whenretracted,

In a first step of the retraction operation, mandrel 8 will be pulledupwardly while guide members 13 and id remain in a fixed position withrespect to the chili collar. Thus on retraction of latching dogs 3d themandrel is free to slide upwardly. However, upward movement of the guidemembers 13 and 14- supporting the cone .cutters is impossible duringthis step of the operation. This is true for the reason that latchingdogs 6 associated with each guide member are essentially wedged in thecircumferential recess 5 of the drill collar so as to prevent upwardmovement of each guide member until latching dogs 6 may be forced intoretracted position.

Consequently on upward movement of the spearhead, mandrel 8 will 'bepulled upwardly until recess 21%. provided in the mandrel registers withlatching dog 6 that is pivotally fixed to guide member 14. Shoulder 26provided on mandrel 8 is positioned to contact shoulder 25 of guidemember 14 when recess 1 registers with latching dog "6. Consequentlywhen the mandrel has been pulled upwardly to this position, shoulder 26hearing against shoulder 25 will force guide member M to move upwardlythrough the drill collar with the mandrel "8. This upward movement ofguide member 14 will force the latching dog 6 associated therewith intothe recess 21 into the position particularly illustrated in Figure 3.The cone cutter it supported by guide member 14 will be free to swinginwardly into the drill collar for upward movement therethrough, againas illustrated in Figure 3.

It will be observed that during this phase of the operation, that iswhen the first guide member and first cone cutter are pulled upwardlyinto the drill collar, the second cone cutter and the guide memberassociated therewith are still maintained in a locked position. Thus thelatching dog 6 that is associated with guide member 13 is wedged inannular groove 5 of the drill collar, preventing movement of guidemember 13 with respect to the drill collar until the recess 20 inmandrel 8 registers with this latching dog. When the mandrel 8 carryingthe first guide member 14 is pulled upwardly sufficiently for recess 2to register with latching dog 6 of guide member 13, shoulder 24 of themandrel will bear against shoulder 23 of guide member 13. Consequentlyin the course of upward movement of mandrel 8, when this occurs, guidemember 13 will be pulled upwardly through the drill string. Latching dog6 mounted on guide member 13 will be forced into the recess 20 asillustrated in Figure 3. The cone cutter 10 supported from guide member13 may then swing inwardly into the drill collar at a position below thefirst cone cutter. The entire apparatus may then be pulled upwardlythrough the drill string with all elements thereof in the retractedposition shown in Figure 3.

The manner in which the retractable drill can be lowcred through thedrill string to assume drilling position will now be described. It isassumed that the elements of the retractable drill are placed in thearrangement shown in Figure 3; in addition latching dogs 30 are closedover the spearhead of a lowering tool and are held in this position bythe inner surface of the drill string and drill collar. The drill islowered through the drill string into the drill collar without change inthe relative position of the elements until the latching dog 6 that isassociated with guide member 13 reaches the lower annular groove orrecess 5 provided in the drill collar. When this occurs, latching dog 6expands outwardly so as to prevent further downward movement of guidemember 13. Mandrel 8 will continue to move downwardly together with thesecond guide member 14. When lowered sufliciently, the latching dog 6that is associated with guide member 14 will similarly expand tolatching position in the annular groove 5 of the drill collar to preventfurther downward movement of guide member 14. At this instant in theoperational sequence, the two cone cutters associated with the guidemembers 13 and 14 will be at the proper horizontal position with respectto drill collar 1. However, the cone cutters will be hanging looselywithin the lower portion of the drill collar. Mandrel 8 is, therefore,forced downwardly, sliding with respect to guide members 13 and 14,until the tapered surfaces provided on the lower termination of themandrel wedge the cone cutter supports against the drill collar. Thisoccurs when the mandrel 8 has been lowered to the position shown inFigure 1 at which position upper latching dogs are enabled to extendinto latching position in the upper circumferential groove 4 provided inthe drill collar. Extension of these upper latching dogs serves to lockthe entire drill in the position shown in Figure l and also serves torelease spearhead 37 permitting removal of the lowering tool.

On then lowering the drill string sufiiciently to cause the cone cuttersto contact the bottom of the borehole, the cone cutters will further bewedged between the mandrel 8 and the drill collar 1 to permit drilling.

While not essential, as shown in Figure 5, an extension or lug 38 may bepositioned in the upper circumferential groove 4 of the drill collar 1.This lug will limit rotational movement of the latches 30 with respectto the drill collar. This serves to prevent rotation of all of the drillelements with respect to the drill collar 1. This will prevent anyrotational slipping prior to the time the cone cutter supports arefirmly wedged between the mandrel and the collar as described. It shouldbe observed, however, that substantially no rotational torque istransmitted through lug 38 during normal drilling operations since thetorque is transmitted directly through the drill collar to the wedgedcone cutters.

A central channel 39 is provided in the center of mandrel 8 associatedwith ports 40 adjacent the cone cutters. Drilling mud may be forcedthrough the drill string and through these ports to lubricate thecutters and flush the cuttings out of the bottom of the hole duringdrilling.

As formerly indicated, while the invention has been described withreference to a drill bit employing two cone cutters, it is particularlycontemplated that the drill bit should employ three cone cutters.Employing the principles described, this is readily achieved bypositioning three equally spaced longitudinal grooves in mandrel 8 inplace of the two described. An additional recess is placed on mandrel 8corresponding to recesses 20 and 21 of Figure 1. This additional recesswill again be at a different level from recesses 20 and 21. Consequentlythese provisions will enable a third drill cone to be suspended belowthe other two in the same manner described. As a practical observationit may be noted that drill cones of larger sizes may be employed whenthree rather than two cone cutters are used. This is possible by virtueof the fact that the conical shape of these cutters acting with the 120spacing around the mandrel permits utilization of somewhat larger conecutters. It should be observed that if desired, latches 30 may be fixedto mandrel 8 in such a manner as to register with the samecircumferential recess that receives the latching dogs 6, thus requiringonly one circumferential recess instead of two, provided that the singlerecess presents both an upward facing facing bearing surface 34 and theupward facing bearing surface 35.

The apparatus heretofore described is preferably provided withadditional apparatus features. These are illustrated in Figure 6. Figure6 illustrates a preferred embodiment of the drill bit showing only theportion of the drill bit above the latching dogs 6. In all otherrespects the drill bit will have the construction which has beendescribed. As illustrated in Figure 6, the mandrel 8 is provided with aseparate section maintained in telescopic sliding relation with theupward termination of mandrel 8 which is cut to have a reduced externaldiameter. Sliding movement of the upper portion 50 with respect to thelower portion 8 is then possible. One or more pins 51 fastened in thetubular member 50 extend into slots 52 positioned in the upper portionof mandrel 8. Slots 52 have sufficient longitudinal length, extendingupwardly and downwardly, to permit limited movement of element 50 withrespect to mandrel 8. A rubber sleeve 53 is positioned on a shoulder ofmandrel 8 just below the lower termination of element 50. This rubbersleeve 53 preferably has an upward and outwardly opening taper at itsupper portion to accommodate the downward and inward taperingtermination of member 50. Thus when member 50 is forced downwardly, soas to slide with respect to mandrel 8, the tapered termination of member50 will force the rubber sleeve 53 firmly against drill collar 1. Thisserves to provide a circumferential seal between the drilling apparatusand the drill collar. The purpose is to prevent by-passing of drillingfluid between the drill collar and the drill bit. All drilling fluid isthus forced downwardly through channel 39 of the mandrel to be suppliedto the cone cutters.

Another preferred feature illustrated in Figure 6 concerns thearrangement of latching dogs 30. As shown in Figure 6, the inner portionof each latching dog 30 is provided with teeth to mate with teethpositioned on the upper termination of mandrel 8. This wickerarrangement, identified by numeral 54, provides an important function.As a practical detail of construction it is undesirable to require thatthe drill bit be machined with such accuracy that latch 30 will justreach operational position when cone cutters 10 are forced into thetightest locked position on lowering of mandrel 8. The wicker referredto serves to eliminate necessity for construction of this precision.Thus the latch 30 in the embodiment of Figure 6 is pivotally supportedon element 50 which in turn fits on mandrel 8, so that the latch 30 willnormally extend somewhat above the recess 4 in which it is intended toseat when the drill bit has been lowered to drilling position.Consequently, on applying downward force on the spearhead employed toposition the drill bit in the drill collar, element 50 may be forceddownwardly suiiiciently to cause the latch 30 to move the remainingdistance necessary to seat in the annular groove 4. This will serve toforcibly extend the packing element or rubber sleeve 53 into sealingposition. Once the latches 30 have been forced downwardly so as to enterthe groove 4, as illustrated in Figure 6, then the teeth of wicker 54-will serve to lock the mandrel in the indicated position when theinsertion force applied by the spearhead is removed.

It is apparent that these and other refinements of the drill bitdescribed may be employed if desired.

As the drill bit has been described, an essential feature of theapparatus includes a suitable insertion and retrieving tool foroperation of the drill bit. Such a tool is illustrated in Figure 7 ofthe drawings. The tool consists of a massive cylindrical element orsinker bar 6%, which may be supported by a cable or wire line 61. Thelower termination of sinker bar is provided With a cylindrical extension62 equipped with a spearhead 37.

Enoircling the cylindrical extension 62 is a larger tubular sleevemember 63 maintained in sliding relation with cylinder 62. A collarelement 64 fixed to sleeve 63 is provided with a conical inner surface65. A threaded opening 66 is placed in collar 64 adapted to accommodatea slotted head set screw 70 which may pass through sleeve 63. When this,set screw 70 is turned into this threaded opening, the shank of the setscrew may extend sufiiciently far to encounter a collar 67 positioned onthe cylindrical extension 62. A coil spring 68 is fixed aboutcylindrical extension 62 so as to act against the lower portion of thesinker bar 60 and the upper termination of sleeve 63. This spring servesto urge sleeve member 63 downwardly with respect to cylindrical support62. However, insertion of set screw 73 in the manner described limitsthis downward movement.

The purpose of this set screw is to hold sleeve 63 and collar 64 in anupward position spaced well above spearhead 37 when desired.Alternatively on retracting the set screw, sleeve 63 and collar 64 maybe forced downwardly toward the spearhead by the spring 68. As will bedescribed, the locked upward position of the sleeve and collar isrequired when using the tool to insert the retractable bit described.However, when retrieving the retractable bit, it is necessary that thesleeve and collar be forced downwardly toward the spearhead.

The retrieving tool as described and as illustrated in Figure 7 is insuitable condition for the lowering of the drill bit formerly described.The latches 30 of the drill bit may be forced inwardly so as to hold thespearhead 37 and will be retained in this position by the internalsurface of the drill string while lowering downwardly to the drillcollar. On reaching the drill collar, latches 30, when they have enteredthe annular groove 4 of the drill collar, will serve to free spearhead37 so that the insertion tool may be removed from the well. In order touse this same tool to retrieve the drill bit, set screw 70 is retractedor removed from the apparatus. Spring 68 can then act to urge collar 64downwardly with respect to the spearhead 37. On then lowering this toolso as to encounter the drill bit, spearhead 37 will first extenddownwardly below the inner shoulders of latch '30 provided by recess 36,while the conical surface 65 of collar 64 serves to force latches 3t)inwardly. On then raising the retrieving tool, the spring 63 will serveto retain latching dogs 30 in the retracted position while maintainingthe latching dogs in locked position with respect to spearhead 37.

What is claimed is:

l. A retractable drill bit comprising, in combination: a tubular drillcollar, at least one circumferential groove within the bore of saiddrill collar providing an upward facing bearing surface and a downwardfacing bearing surface, a cylindrical element fitting slidably withinsaid drill collar, the lower outer contour of said cylindrical elementhaving a downward and inward taper, said cylindrical elementhaving atleast two circumferentially spaced longitudinal slots each provided withan upward facing projection adjacent the lower end of said cylindricalelement, at least two elongated drill cutter supports, each positionedin one of said longitudinal slots in sliding relationship between saidcylindrical element and said drill collar, eacl". of said drill cuttersupports having a downward facing shoulder engageable with said upwardfacing projection in said longitudinal slot, a first downwardlydepending latching means pivotally fixed to each of said cutter supportsand engageable with said upward facing bearing surface, said drillcutter supports including means adapted to receive said latching meansin a manner permitting movement of said cylindrical element within saiddrill collar, means urging the lower end of each of said first latchingmeans outwardly, a second latching means pivotally fixed to saidcylindrical element and engageable with said downward facing bearingsurface to limit upward movement of said cylindrical ele- 75 meat withrespect to the drill collar, said cylindrical element including meansadapted to receive said second latching means in a manner permittingmovement of said cylindrical element with respect to the drill collar,means urging said second latching means outwardly, and a drill cutterelement suspended from each of said supports, each of said cutterelements having an inward facing portion having a contour adapted toengage the lower outer contour of said cylindrical element, said firstlatching means being so positioned on said cutter supports that saidcutter elements will be placed adjacent the lower end of said drillcollar when said first latching means engages said upward facing bearingsurface, said second latching means being so positioned on saidcylindrical element that the lower tapered portion of said cylindricalelement will be positioned to bear against said inward facing portionsof said cutter elements, forcing said cutter elements against the lowerend of said drill collar when said second latching means bears againstsaid downward facing bearing surface, to thereby prevent upward movementof said cylindrical element and said cutter elements during drilling,the said forcing of said cutter elements against said drill collarthereby providing for transmission of torque from said drill collar tosaid cutting elements, said second latching means being positioned onsaid cylindrical element in a manner providing access to said secondlatching means by latch disengaging means lowered into said drill collarabove said cylindrical element, whereby said second latching means maybe disengaged from said downward facign bearing surface by a toolinserted in the drill collar, said cylindrical element may then bepulled upwardly out of engagement with said cutter elements, saidcylindrical element being slidable upwardly with respect to said cuttersupports until said upward facing projections in said longitudinal slotsengage said downward facing shoulders on said cutter supports, therebypulling said cutter supports upwardly as said cylindrical element israised, and drawing said first latching means out of engagement withsaid upward facing bearing surface, whereby said cutter supports andcutter elements may be retracted through said drill collar.

2. Retractable drill bill as defined by claim 1 wherein the lower innercontour of said drill collar has a downward and outward taper.

3. Retractable drill bit as defined by claim 1 wherein each of saidfirst latching means includes an inward extension and wherein saidcylindrical member includes a recess to receive each of said inwardextensions, said recesses being so positioned with respect to saidupwardly facing projections of said longitudinal slots that said inwardextensions can enter said recesses only when said upward facingprojections are adjacent the downward facing shoulders of said cuttersupports.

4. Retractable drill bit as defined by claim 1 wherein each of thedownward facing shoulders of said cutter supports is placed at adifferent distance from its associated cutter element than each of theother downward facing shoulders, whereby said cutter elements will beretracted separately as said cylindrical element is raised in the drillcollar.

5. Retractable drill bit as defined by claim 1 including an inwardextension held by said drill collar and positioned adjacent saiddownward facing surface within said circumferential groove adapted toengage said second latching means against rotational movement, wherebyto limit relative rotational movement of said cylindrical element andsaid drill collar.

6. Retractable drill bit as defined by claim 1 wherein threecircumferentially arranged longitudinal slots, three drill cuttersupports, three first latching means and three drill cutter elements areprovided.

Hurley July 16, 1940 Walker Oct. 10, 1944

